Compounds of Zinc, Cadmium and Mercury

J. L. Wardell, Organometallic Compounds of Zinc, Cadmium and Mercury, Chapman Hall, London, 1985,... 

Zn(R-dtp)2 complexes have been characterized and their thermal stabilities investigated 173,184,190,297-299,301-305) Zn(R-dtp)2 compounds are thermally degraded to volatile olefins and non-volatile residues and this serves as the basis for gas chromatographic determination of the compounds 304,30s) Several papers describing pyrolyses of Zn(R-dtp>2 complexes have discussed mechanisms for formation of olefins, sulfides, and other products 173,184,190,298,299, 304) Dakternieks and Graddon i8s,283)35 mentioned earlier, have reported thermodynamic measurements for depolymerization and adduct formation reactions of zinc, cadmium and mercury R-dtp compounds. 

Stepwise stability constants for complexation between Zn2+ and Cd2+ and the acids X(CH2CH2C02H)2 (X = 0, S, Se or Te), Se(CH2C02H)2, X(CH(Me)C02H)2 (X = S or Se) and H02CCH2SCH2CH2C02H have been measured.882 The structures of benzeneselenic acid complexes of zinc, cadmium and mercury have been investigated by IR spectroscopy the bonding of the areneseleninato ligand depends on the water content of the compound. The hydrated complexes are always of the 0,0-type the anhydrous complexes are mainly 0,0... 

Sapozhnikov and Markovskii measured at 298.15 K the enthalpy of dissolution of a number of zinc, cadmium, and mercury selenites in mineral aeid in a calorimeter. Sulphuric acid (aq, 1 50) was used for the zinc and cadmium compounds, while hydrochloric acid (aq, 1 35) was used for the mercury salts. The experimental details are few and... 

The first four members of Division B show a striking family resemblance, with gradual changes in properties. Mercury in many respects resembles copper, as for example in the numerous ammoniacal compounds formed. Zinc, cadmium, and mercury form a typical triad beryllium and magnesium resemble each other closely and form a connecting link between the alkaline earths and the zinc sub-group. The vapors of all five metals of this division are composed of monatomic molecules. The physical properties are shown in Table XV. 

No monomeric alkali metal alkyls or aryls are known, as those crystal structures which have been determined indicate electron-deficient, e.g. (MeLi), or ionic (K Me ) constitutions. The dialkyls of the lighter second group metals are mostly electron-deficient dimers or polymers, but those of zinc, cadmium and mercury are monomers with a linear structure as expected from participation of one (metal) s and one p orbital (with or without dji participation). In the third group the pattern is more complex. Whereas the trialkylboranes are monomeric, boron hydrides (and alkyl hydrides) and polyboron compounds form electron-deficient structures. Aluminium alkyls and alkyl hydrides are normally electron-deficient dimers or trimers gallium trialkyls are monomeric though the trivinyl is a dimer trimethylindium is a weakly associated tetramer in the solid state, otherwise all indium and thallium trialkyls appear to be monomers. 

Zinc, cadmium and mercury are at the end of the transition series and have electron configurations ndw(n + l)s2 with filled d shells. They do not form any compound in which the d shell is other than full (unlike the metals Cu, Ag and Au of the preceding group) these metals therefore do not show the variable valence which is one of the characteristics of the transition metals. In this respect these metals are regarded as non-transition elements. They show, however, some resemblance to the d-metals for instance in their ability to form complexes (with NH3, amines, cyanide, halide ions, etc.). 

On the other hand, the binary compounds of sodium with zinc, cadmium, and mercury, or with tin and lead, have no such analogies with one another. The sodium compounds of bismuth and antimony are analogous, but the characteristics of these latter elements approximate to those of the metalloids,... 

The (/-block elements tend to lose their valence s-electrons when they form compounds. Most of them can also lose a variable number of d-electrons and show variable valence. The only elements of the block that do not use their (/-electrons in compound formation are the members of Group 12 (zinc, cadmium, and mercury). The ability to exist in different oxidation states is responsible for many of the special properties of these elements and plays a role in the action of many vital biomolecules (Box 16.1). 

Copper, silver, and gold in Group I show a similarity to sodium and potassium principally in the fact that they form certain compounds of the same type, for example, M20 and MCI. Zinc, cadmium, and mercury in Group II resemble calcium, barium, and strontium in that they form compounds of the types MO, MSO4, MC12, etc. In other respects, the divergence in the properties of the elements of the A and B Families is at a maximum in these two groups. 

Tossell, J. A., and D. J. Vaughan (1981). Relationships between valence orbital binding energies and crystal structures in compounds of copper, silver, gold, zinc, cadmium and mercury. Inorg. Chem. 20, 3333-40. 

Dialkyl derivatives of elements of the Second sub-Group, namely, zinc, cadmium, and mercury, contain an almost completely covalent metal-carbon bond. These compounds are normal, unassociated liquids with low boiling points e.g., the dimethyl derivative of zinc boils at 46°, that of cadmium at 105.5°, and that of mercury at 92°. 

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